<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
        var a = 10,
            b = 11,
            c = 12;

        function test(a) {
            a = 1;
            var b = 2;
            c = 3;
        }
        test(10);
        console.log(a); // 10
        console.log(b); // 11
        console.log(c); // 3
    </script>
</body>

</html>